arch-arm: Faults DebugFlag now printing inst opcode if available

arch-arm: Faults DebugFlag now printing inst opcode if available

This makes it easier to debug unimplemented instructions.

Change-Id: Iaaa288037326722f07251299fd68eacb2e295376
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Ciro Santilli <ciro.santilli@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/18396
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>